In order to reduce harmonic distortions caused by power electronics devices on power system, a power factor correction (PFC) circuit can be used to achieve a good power factor by controlling an AC current in sinusoidal and in phase with the AC voltage. The most common type of PFC circuit is a boost converter. In high power applications, an example boost converter operable in a continuous conduction mode (CCM) is shown in FIG. 1. The example of FIG. 1 can include a power stage circuit and a pulse width modulation (PWM) controller. The power stage can be a boost converter including inductor L, power switch QM, diode D, input capacitor C1, and output capacitor C2.
The PWM controller with current and voltage loops can include: (i) an output voltage feedback loop used to detect output voltage Vout and generate output voltage feedback error signal Vcomp; (ii) a multiplier used to generate reference signal Vr according to a rectified input voltage Vg and output voltage feedback error signal Vcomp; (iii) an inductor current sampling circuit Rs used to obtain sampling voltage signal Vsen through averaging the detected inductor current signal Ig; (iv) an operational amplifier W1 used to generate error voltage signal Verr by comparing and amplifying sampling voltage signal Vsen and reference signal Vr, where sampling voltage signal Vsen is received at its inverting terminal and reference signal Vr at its non-inverting signal; and (v) a PWM logic controller used to generate a switch controlling signal for power switch QM by comparing error voltage signal Verr against a saw-tooth wave, where the saw-tooth wave can be generated by an oscillator.
By controlling the PFC circuit in an average current mode, the current from the AC line can be sinusoidal and in phase with the AC voltage to achieve a good power factor. However, in such a conventional PWM controller, an oscillator may be needed to generate a saw-tooth wave with a fixed clock frequency to obtain a fixed operating frequency for power switch QM. Also, in order to generate reference signal Vr, it may be necessary to detect input rectified voltage Vg, which may increase the pin count of the PWM controller. Therefore, such conventional approaches may be more complex and expensive when designing a CCM boost PFC controller.